Electrocardiography has achieved a significant degree of medical success in the recording and analyzing of the electrical currents produced by the animal and human heart muscle when it contracts and instruments commonly called electrocardiographs have been devised to receive these electrical impulses and record them on an electrocardiogram, usually with a stylus and web-type graph paper, although in recent years cathode ray tubes have been employed to display the electrocardiogram signal. The waveform consists of a complex of waves commonly referred to as the PQRST complex. The initial P-wave represents the beginning of auricular activity and the QRST-waves together represent the onset and procession of ventricular contraction. This information is useful in telling the state of the heart muscle and in diagnosing disturbed heart rhythms. At times it can indicate non-specific heart muscle damage and in other cases it can also diagnose the source of the damage as in coronary thrombosis.
Electrocardiogram instruments insofar as they relate to the signal processing of the electric currents produced by the heart muscle as well as the manner of displaying the signal as processed to the physician have been largely unchanged for the last twenty years, with the exception of the advent of solid-state and IC technology which have simplified and reduced the cost of these instruments but have not significantly modified the signal processing and display functions.
This has been the case in spite of the fact that there has been a profound need to improve the communication link between the EKG monitoring device and the physician. One attempt to improve this communication link has taken the form of a telephone system that enables the EKG waveform to be transmitted over conventional telephone lines into a receiving circuit where the signal is reproduced by a secondary signal demodulating system that usually includes a conventional stylus and web graph paper feeding device for display purposes. Such telephonic monitoring devices are exemplified in the Gombrich et al. U.S. Pat. No. 3,920,005, the Malchman et al. U.S. Pat. No. 3,872,252 and the Pori U.S. Pat. No. 3,886,314. While such telephonic transmission systems have found a reasonable degree of commercial success, all these systems presently known require a receiving demodulating and display device at the telephone receiving location and thus the physician, unless he carries this receiving instrumentation from location to location, is unable to demodulate the EKG signal transmitted with conventional telephone equipment.
There have also been developed in the last decade several fairly sophisticated systems for verifying certain segments of the EKG waveform such as the QRS segment by comparing the segment configuration with stored reference signals, and upon verification storing those so verified and blanking those not verified. Such a system is shown in the Jirak U.S. Pat. No. 4,367,753; however the Jirak system like similar prior EKG monitoring devices uses only conventional display techniques such as an analog chart recorder for displaying the information stored.
Other devices that verify portions of the patient's EKG waveform to compress data or to develop R or S wave peak detection to determine heart rate are found in the Day et al. U.S. Pat. No. 4,109,243 and the Levin U.S. Pat. No. 4,250,889. But again, neither of these proposes any system for altering conventional communication techniques between the EKG signal processing circuitry and the physician.
It is the primary object of the present invention to improve the EKG monitoring and communication systems known in the prior art and discussed generally above.